This invention relates to an electric connector suitably used for connecting a flexible flat-type wiring member (such as a flexible printed wiring board having a plurality of conductor patterns formed on an end portion thereof and a flexible flat cable) to a circuit board such as a printed circuit board and a flexible printed wiring board.
Flat-type wiring members (hereinafter referred to as “FPC”), which are thin and flexible and in which conductors can be provided at a small pitch, have been extensively used as wiring members in electronic equipments which have now been formed into a more compact design and a thinner design.
In one conventional method of connecting this FPC to a circuit board such as a printed circuit board (printed wiring board), a socket member is mounted on the circuit board, and a terminal portion of the FPC is soldered to a plug member which is adapted to be inserted into the socket member to be electrically connected thereto. In this method, however, the operation for soldering the FPC requires much labor and time, and therefore is not easy. In order to solve this problem, Japanese Patent Publication No. 7-22127A discloses an electric connector in which an FPC is connected to a plug member without the need for a soldering operation.
The structure disclosed in this publication includes: a plug member having a laterally-extending portion and a vertically extending portion so as to form a generally inverted L-shaped cross-section or a T-shaped cross-section; and plug contact pins provided in contiguous relation to a lower face of the laterally-extending portion and each side face of the vertically-extending portion; and a plug cover disposed in opposed relation to the laterally-extending portion of the plug member. The vertically-extending portion of the plug member is inserted into a socket member, and a terminal portion of an FPC is held between the plug cover and the laterally-extending portion of the plug member.
With this construction, the laterally-extending portion of the plug member presses generally V-shaped contact portions of laterally-extending portions of the plug contact pins. The laterally-extending portions of the plug contact pins can be brought into press-contact with the terminal portion of the FPC to be electrically connected thereto, and therefore the operation for connecting the plug contact pins to the terminal portion of the FPC can be easily carried out without the need for a cumbersome operation such as a soldering operation.
Japanese Patent Publication Nos. 8-195256A and 9-28323A disclose other examples which enable electrical connection without the need for soldering a terminal portion of an FPC. In these examples, a gap is formed in each contact pin, and the terminal portion of the FPC is inserted in this gap, and in this condition a pressing member is operated to be pivoted about one side portion of the gap serving as a fulcrum, so that the terminal portion is biased and pressed against an inner face of the other side portion of the gap. By thus operating the pressing member, the terminal portion of the FPC can be easily electrically connected to the contact pins.
In electronic equipments which have now been formed into a more compact design and a higher-density design, the structure of connecting a circuit board (such as a printed circuit board within these electronic equipments) to the FPC has been more and more required to have a thin (low-height) design and a multi-terminal design (i.e., increasing the number of terminals of the FPC). Naturally, it is desirable that this connecting operation can be carried out easily, and it is also desirable that the connecting structure, even when having the multi-terminal design, can meet the requirement of the thin design.
In the example disclosed in Japanese Patent Publication No. 7-22127A, in order to ensure the connection (electrical connection) of the FPC to the plug member, it is necessary to impart a certain press-contacting force (holding force) produced as a result of resilient deformation of the generally V-shaped contact portions of the laterally-extending portions of the plug contact pins to the connecting portion thereof. In the case of increasing the number of socket contact pins and the number of plug contact pins corresponding thereto (that is, in the case of providing a multi-terminal design), it is naturally necessary to increase the overall press-contacting force of the connector produced by all of the plug contact pins in proportion to the number of the plug contact pins.
However, the increased overall press-contacting force in this multi-terminal form incurs increased stresses acting on the laterally-extending portion of the plug member which is made longer in the direction of arrangement of the plug contact pins as a result of the multi-terminal design. Thus, the laterally-extending portion is subjected to a reaction force of the overall press-contacting force, and as a result there is a case that it is warped. Particularly, an intermediate portion of the laterally-extending portion remote from portions of the plug member which are retainingly engaged with the plug cover is raised. Therefore, the pressing force of the laterally-extending portion of the plug member, which is applied to the laterally-extending portions of the plug contact pins, is reduced, thereby making the electrical connection achieved by the press-contact unstable.
A simple method of preventing this disadvantage is to increase the thickness of the laterally-extending portion of the plug member (that is, the thickness between the upper and lower face of the laterally-extending portion). However, the increased thickness of this laterally-extending portion leads to an increased size of the plug member in the vertical direction, which makes it difficult for the connector to meet the requirement of the above-mentioned thin design.
In addition, the ability of retaining the FPC against withdrawal when a pulling force is applied laterally to the FPC held between the plug cover and the laterally-extending portion of the plug member is correlated with a frictional force of this retaining portion which is obtained by multiplying the above press-contacting force by a constant friction coefficient. On the other hand, a method of reducing the thickness of the laterally-extending portion of the plug member in the vertical direction is advantageously used for meeting the requirement of the above thin design. However, when the laterally-extending portion of the plug member is made thin, the rigidity of this laterally-extending portion is lowered, and the pressing force required to hold down the contact portions of the plug contact pins to be brought into press-contact with the terminal portion of the FPC, as well as the frictional force related thereto, is reduced. The reduced frictional force adversely affects the FPC-retaining function, and leads to adverse effects on the connecting reliability such as deviation of the connecting position and the accidental withdrawal of the FPC. Therefore, it is difficult to achieve the multi-terminal FPC-connecting electric connector which has a thin design and a high connecting reliability.
In the examples disclosed in Japanese Patent Publication Nos. 8-195256A and 9-283237A, the terminal portion of the FPC is caused to abut against the inner face of the other side portion of the gap of each contact pin by the force applied by the pressing member which is pivoted about the one side portion of the gap serving as a fulcrum. Therefore, the force to cause the terminal portion to abut against the contact pins will not vary in accordance with the arrangement position of the terminal portion as in the example disclosed in Japanese Patent Publication No. 7-22127A. However, even in these examples, the FPC-retaining ability depends only on the frictional force corresponding to the force to grip the terminal portion of the FPC, and therefore has been found not entirely sufficient.